1. Field of the Invention
The invention relates to crosslinkable materials which are based on organosilicon compounds and which cure preferably to form materials of reduced modulus, to processes for producing them, and to their use.
2. Description of the Related Art
One-component silicone rubber mixtures which vulcanize to form elastomers at room temperature (RTV1) on ingress of water, and which are storable in the absence of water, are known. These products are used in large quantities, for example, as joint-sealing compounds in the construction industry. The basis for these RTV1 mixtures are polydiorganosiloxanes, terminated either with OH groups or with silyl groups which carry hydrolyzable groups. Through the chain length of the polymers it is possible to influence key properties of the RTV1 mixtures. The so-called modulus in particular, usually reported as secant modulus at an elongation of 100%, can be regulated by the chain length. For joint-sealing compounds in particular it is desirable for this modulus to be low, to minimize forces acting on the edges of the joint. For economic and technical reasons, however, there is only a limited range of polymer chain lengths available for the production of RTV1 mixtures. The high chain lengths that are necessary for very low-modulus sealants, in particular, result in very high viscosities on the part of the polymers, and so, because of the resultant stiff paste consistency, the ready-to-apply products require high forces for extrusion from the cartridge, and hence are hampered by disadvantages in processing.
Adjusting or lowering the modulus is a frequent topic of description in the patent literature. CA 2056487 A2 proposes incorporating mono-alkoxy-functional end groups into the polymer. These groups no longer exhibit virtually any reaction, and so lower the modulus. The latent alkoxy groups are a disadvantage in that they nevertheless display residual activity under elevated temperature and humidity influence, and may have adverse consequences for the vulcanizate properties.
EP-A 0776944 describes monofunctional siloxanes which exhibit adjustment of modulus non-functional terminal groups. While this does avoid the disadvantage of CA 2056487 A2, it nevertheless necessitates a separate, targeted preparation of such monofunctional siloxanes.
In order to avoid these difficulties, the principle of chain extension has been pursued for adjustment of modulus. U.S. Pat. No. 5,110,967 describes Si—N heterocyclic silanes, but specialty crosslinkers of this kind are not available on the market. Further difunctional silanes have been described in U.S. Pat. No. 5,290,826 (bisacetamidosilanes), DE 12 95 834 (bisacetoxysilanes), and EP 74 001 (bisaminosilanes), but these release basic or acidic elimination products and are therefore not suitable for surfaces which are not compatible with these elimination products. This is the case, for example, for marble or some metallic surfaces. Chain extension with acetamidosilane or aminosilane, moreover, still gives rise to an odor nuisance.
Difunctional dialkyl-dialkoxysilanes do not give off any corrosive byproducts, but are unsuitable, since they exhibit inadequate reactivity and display a significant effect only when added at a very high level, this being a disadvantage in terms of cost. In this regard, see U.S. Pat. No. 5,300,612, U.S. Pat. No. 5,470,934, and DE-A 198 55 619. EP-A 0575863B1 and EP-A 0 693 533 attempt to resolve this disadvantage by using short-chain siloxanes having two in-chain alkoxy functions. However, such siloxanes must be specifically produced and are still always too unreactive. Accordingly, they as well must be used in relatively large quantities. EP-A 1006146 describes mixed endblocking with a mixture of di- and trifunctional alkoxysilanes, with which a moderate modulus reduction effect can be obtained only by using comparatively large quantities of difunctional dimethoxydimethylsilane. This increases the weight loss and the emission of elimination products, and is detrimental to cost.
JP 63-83167 describes chain extension using difunctional α-amino-substituted alkoxysilanes, with distinct effects. The disadvantage of the proposed formulas, however, is the high quantity of difunctional α-silane, which has serious disadvantages in terms firstly of cost and secondly of shelf life. EP 1 735 369 B1 describes siloxanes having the feature of particularly quick-crosslinking preparations. These are based on pure α-aminosilane functionalization or else on mixed endblocking with secondary α-amino groups. The storage stability in the vulcanizate, however, is poor.
EP-A 1431330 describes an attempted solution with which good modulus adjustment results were achievable with low quantities of α-aminofunctional alkoxysilanes, but the storage stability could not be stabilized until isocyanate compounds were added. This is critical on account of the toxicity of isocyanates, and therefore has adverse consequences for the production and handling of such preparations.
The problems addressed by the invention are to provide crosslinkable compositions with a modulus which can be adjusted by targeted chain extension, which are largely isocyanate-free, and which at the same time are stable on storage and have good workability.